I get asked this a lot, and now it’s a tip: how do I put a line break in a formula inside a cell to make it easier to edit?
The answer is, while editing the formula, use Alt-Enter to put in the line breaks.
There are pros and cons to this.
The pro is that if you like to edit formulas in cells (say by clicking F2), the line breaks are really helpful.
The con is that if you like to edit formulas in the formula bar, only one line will appear at a time. You can scroll through them with the arrow keys, but it can be disconcerting.